Extremely high frequency (EHF) is a form of electromagnetic radiation that ranges in frequencies from 30 to 300 GHz. The EHF band is also known as the millimeter wave band, as radio waves within this band have wavelengths from 1 to 10 millimeters. Radio signals in this band are extremely prone to atmospheric attenuation. In particular, signals in the 57-64 GHz range are absorbed by oxygen molecules, which limits propagation of EHF signals in this frequency range to a few kilometers. As such, the FCC has made the 57-64 GHz band available for use by unlicensed devices. The actual absorption coefficient (signal attenuation per kilometer) depends on the signal frequency and on certain atmospheric conditions, including humidity, barometric pressure, and presence and type of precipitation.